Looks like it could be a memory failure.
If all the RAM is on removable sticks, try removing and reseating it.
You can get RAM testing software such as
http://www.memtest86.com - boot from the CD and run the diagnostics.
If you can identify a duff RAM stick you could just replace it.
Worst case is your PC needs to be repaired or replaced. However, the hard disk should be OK, so your data should be safe. Put the disk in an external USB caddy, or hitch it up to a 2.5-3.5" IDE adapter in a desktop PC.
SD